System for monitoring traffic conditions in connection with the control thereof

ABSTRACT

A system for monitoring traffic flow on streets having at least two traffic lanes free from oppositely directed traffic, particularly highways, wherein each traffic lane can be monitored, at least at one common location, by respective vehicle detectors, in which the magnitudes of time intervals between successive vehicles at the associated detector are measured, and mean values thereof are formed, together with mean values of another representative corresponding magnitude between successive intervals, with the values being stored in respective memories and supplied therefrom over linking means with a differenceforming device, together with similar values from other detectors, in predetermined timing with the output of the difference-forming device providing an evaluatable magnitude related to the traffic flow.

United States Patent Kohnert Sept. 16, 1975 [54] SYSTEM FOR MONITORING TRAFFIC 3,506,808 4/1970 Riddle et a]. 340/31 A IN WITH TliE 3,613,074 10/1971 Hill et 3.1. 340/37 3,710,081 1/1973 ApitZ 340/31 A CONTROL THEREOF Primary Examinerl(athleen H. Claffy [75] Inventor: Dietrich Kohnert, Eichenau,

Germany Assistant ExaminerRandall P. Myers [73] Assignee: Siemens Aktiengesellschaft, Berlin & Attorney Agent or F 1 Gross slmpson Van Munich Germany Santen, Steaclman, Chrara & Simpson PP 332,258 A system for monitoring traffic flow on streets having at least two traffic lanes free from oppositely directed [30] Foreign Application Priority Data traffic, particularly highways, wherein each trafiic lane F b 17 1972 G 2207487 can be monitored, at least at one common location, by e emany respective vehicle detectors, in which the magnitudes of time intervals between successive vehicles at the as- [Z?] 340/38 Ragga/31101: sedated detector are measured, and mean Values 'f i 37 thereof are formed, together with mean values of an- [5 1 le 0 care L 3 other representative corresponding magnitude between successive intervals, with the values being stored in respective memories and supplied therefrom [56] References cued over linking means with a difference-forming device, UNITED STATES PATENTS together with similar values from other detectors, in 3.234505 2/1966 Du Vivier 340/37 predetermined timing with the output of the differ 3,241,109 3/ 1966 Du Vivier.... 340/37 ence-forming device providing an evaluatable magni- 3,416,130 12/1968 Brockett 340/37 mde related to the traffic fl 3,466,599 9/l969 Clark et al. 340/37 3,501,763 3 1970 Preti 340/38 R 23 lai 4 r wing F g DETECTOR 2335? I 26 we M I e Amus'r.

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a I n a n 3 MEAN VALUE suoormus p FORMING 05v. mm: as I W? R Zn=Za+a1lZn-Za| REGISTER n 3 P82 Sn REGISTER REGISTER u PRODUCT w .a-Zn-Sn K 1 MW3 m DIFFERENCE OUOTIENT roimmu [1 soamus DEVICE mam VALUE FORMING DEV I id 3 SNOOTHING FACTOR EVALUATION SYSTEM PATENIEB SEP 1 5 ms SHEET 1 0F 2 Fig.1

MONITORING STATION MONITORING STATITJTJ STATIONARY fossmucnou DETECTORS/C DETECTORS PATENTED SEP I 6 I975 SHEET 2 2 DETECTOR MEASURING SYSTEM COUNTER-\ r RESET ZM REGISTER Za gnu/Imus 222%? Zn I PEI/(ZEN:S

gf; Zn-ZaI n REGISTER MEAN VALUE SMOOTHING I FACTOR FORMING DEVICE MEAN VALUE FORMING DEV.

- R I 7n=7a+ 1 [Z -2'5 REGISTER Sn REGISTER REGISTER f1 PRODUCT I K K3 a1 Z S FO R II NG DIFFERENCE \{QUOTIENT FORMIND FORMING DEVICE MEAN m ggy DEV.

FORM

SMOOTHING l FACTOR C EVALUATION SYSTEM TIMING GEN.

SYSTEM FOR MONITORING TRAFFIC CONDITIONS IN CONNECTION WITH THE CONTROL THEREOF BACKGROUND OF THE INVENTION The invention is directed to a system for use in de picting and controlling traffic operations on streets utilizing at least two traffic lanes which are free from traffie in the opposite direction, such as highways, and from which desired indications and control of traffic may be effected, with each traffic lane being monitored by a traffic detector at least at one common monitoring or measuring location. As traffic continually increases in density, even on highways, traffic surveilance and monitoring, similar in manner to that utilized in cities becomes of greater and greater importance, particularly in connection with possible control by means of speed indicators and other devices. It is known in the prior art to direct a part of the traffic to exits when an undesirable density is reached, whereby relief can be effected. It has heretofore been deemed necessary to detect the traffic on the highway, if possible over the entire range or distance, and it is already known to direct television cameras at suitable observations points and to channel the evaluation information to a central office. As control personnel are required in such operations, other solutions have been sought, i.e., measuring or monitoring locations with traffic detectors at suit able intervals to detect vehicles entering or leaving such areas and to utilize data so obtained in the formation of conclusions as to the traffic density and other traffic conclusions from differences therebetween. As previously mentioned, with the first method, substantially continuous observation by personnel is required, but while the second method does not require such observation, it is possible with such system not to detect vehicles while they are driving in or out, whereby entirely erroneous information will be transmitted due to the addition of errors.

SUMMARY OF THE INVENTION The invention is directed to the production of a system for monitoring traffic on streets where at least two traffic lanes are free from traffic in the opposing direction, preferably a highway, which is simple in construction and does not contain the above referred to disadvantages, and which will make accurate reflections of the traffic flow on the highway.

These results that are achieved by the utilization of a traffic detector for each traffic lane, at at least one common monitoring location, and utilizing a measuring device for determining the duration of time intervals between vehicles. Means are provided for determining the mean value of such intervals and also the mean value of an additional representative magnitude such as the difference between a first monitored interval and a newly monitored interval, preferably modifying such additional value, for example by squaring the same, prior to deriving the mean value thereof and with the employment of associated memories for each traffic detector, and a difference-forming device. the contents of such memories along with the associated memories of other traffic detectors. being interlinked over product-forming devices, under the control of timing means, will result in the formation by the differenceforming device of an evaluatablc magnitude relating to the traffic flow, and by means of which obstructions to the normal flow, either stationary or slowly moving, may be ascertained.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings wherein like characters indicate like or corresponding parts:

FIG. 1 schematically illustrates a section of a roadway and associated traffic detectors;

FIG. 2 is a circuit diagram of a system embodying the present invention with, however, circuit details individual to the respective traffic detectors being illustrated only for traffic detector 1;

FIG. 3 is a chart illustrating changes in traffic distribution; and

FIG. 4 is a graph of the favorable operational range of the system.

DETAILED DESCRIPTION OF THE INVENTION FIG. 1 illustrates a section SA of a highway, compris ing two traffic lanes, FI and F2, having a single traffic direction as illustrated by the arrow P. Two monitoring locations A, B are employed, provided with traffic detectors 1-4, detectors 1 and 3 being associated with lane F1 and detectors 2 and 4 being associated with lane F2, with the distance between the locations A and B being approximately 500 to 1,000 meters. The four traffic detectors 14, in conjunction with the circuit shown in FIG. 2, permit the monitoring of the traffic conditions along the section SA, by means of which suitable indicator" and control means may be adjusted or controlled. In addition FIG. 1 also illustrates a stationery obstruction Hi which is positioned on the right side of traffic lane FI.

FIG. 2 primarily illustrates the circuitry associated with the single detector 1, and as hereafter discussed in greater detail like circuitry is provided for the remaining detectors.

During each occupancy of the detector I by a vehicle, a vehicle impulse will be produced, which will be conducted to a measuring device M, and which in turn controls a timing generator ZG. The latter is operative to produce impulses, for example of 20 m/sec, and delivers them to a time measuring unit ZM, which may be in the form of a counter, and will count the number of impulses from generator ZG, following triggering of the device M by the vehicle, until another vehicle occupies the detector 1. Upon the receipt of the new vehicle impulse at the measuring device M, the time measuring device ZM will be reset, over the timing generator ZG, to zero and the time total of the counter ZM will be si multaneously conducted to a mean value forming device MWI.

The signal thus transmitted to the device MWI represents the time duration of the interval between two vehicles. To avoid the possibility of false indication due to long time intervals, a suitable time control tm may be provided in connection with the time generator ZG. to provide an impulse after a predetermined time in the event no vehicle impulses have been received within the specified time period. The measuring device M, timing generator ZG, measuring device ZM and timing control t m may collectively be termed the measuring system." The respective time intervals, arriving successively, are averaged in the mean value forming device MWI and the results are stored in memories, comprising respective registers RI and R2, after the arrival of each new time interval, for further evaluation.

In this connection, difference-forming means is provided in the mean value forming device MWl, which will initially form the difference between the old mean value Za of a time interval and the new time interval Zn. This difference (Zn Za) is then multiplied by a factor a 1 by means of a product generator associated with the meanforming device MWl whereby the mean value Zn at the output of the latter is equal to Za a 1 (Zn Za), and is added to the contents of registers R1 and R2 for storage, whereby the register R1 stores the value Za and the register R2 stores the value Zn.

Simultaneously, the difference (Zn Za) is conducted to modifying means comprising a productforming device PBl, which is illustrated as being in the form of a squaring device, whereby there appears at the output thereof the value (Zn Za) which represents the difference value Sn. The output of the squaring device PBl is supplied to a second mean-forming device MW2 which operates in the same manner as the device MWl, but as will be apparent from the circuit, operates with the factor a 2. The results thereof are stored in the respective registers R3 and R4, with the register R3 storing the last or preceeding mean value Sa while the register R4 stores the new or latest mean value Sn.

The contents of the registers R2 and R4 are supplied to a product-forming device PB2 operable under the control of a timing generator TG, which provides an interrogation impulse, for example, every 60 seconds. As a result, a product a is formed by the described circuitry from the mean time interval Zn and the mean time difference Sn for the detector 1, under the control of the timing generator TO.

The circuitry, thus far described with respect to the detector 1 is duplicated for each of the other detectors 2-4 whereby similar products will be produced for each of the other detectors. The product a, from the product-forming device PB2 is conducted to a quotientforming device QB, the other input of which receives the product a from the corresponding product forming device PB2, associated with the circuit of the detector 2. The quotient values Kn are supplied to a third mean value forming device MW3, which device is similarly constructed to the devices MWl and MW2 and thus provides a mean value Kn (A) of the quotients Kn of the measuring values received from the detectors 1 and 2 at each interrogation impulse from the monitoring location A. The mean value Kn (A) is conducted to a difference-forming device DB1 and to a register R5, which is operable to store the previous quotient Ka. In like manner the mean value Kn (B) of the quotient Kn, derived from the detectors 3 and 4, at the monitoring location B, will be derived from a corresponding mean value forming device and associated circuitry.

It will be appreciated from the above description that the product-forming device PB2, quotient-forming device QB, means value forming device MW3 and associated circuitry thus form linking means for memories R2 and R4 as well as linking means (at a; of QB and Kn( B) at DB1 for detectors 3 and 4 from monitoring location B with detectors 1 and 2 from monitoring location A.

Thus the detection and measurement of the following magnitudes involved in the arrangement of FIG. 1 is assured, and may be illustrated in the following tabulation:

1. Average time gaps:

Z Z 2 Z, and therefrom II. Variation of the time gaps:

S S S S and therefrom S XA z n, YA B If an obstacle is present in the case illustrated, the following will be applicable:

Due to density fluctuations caused by lane ZIL'I rll changes lt-l .12

lI-l 12 and Since S involve free traffic of fairly small density and S, involves forced traffic of higher density YR YA also X Y =K X Y K,

Thus, the difference of the quotients Kn (A);Kn (B) is formed every seconds and is supplied to an evalu ation system AW. As it has been explained, this difference thus is an evaluatable magnitude, representative of the obstructed condition of the traffic path SA. No obstacle is present in the case of a different zero value, whereby each deviation from the zero value serves as a measure or evaluation of the obstruction.

Additively, a difference of the quotients (Kn Ku) of a monitoring location A (or, of course, of other monitoring locations such as B) can be formed for each individual measuring loctions such as A, between two or several successive interrogation intervals, for example, by a second difference forming device DB2, and thus conclusions may be obtained with respect to the measurement of the time change of the obstruction. in order to differentiate between locally fixed and mobile obstructions Hi, the first differences are taken into account accordingly, with respect to space and location. As can be described in detail from the following tabulation:

Locally fixed obstructions and moving obstructions The following is applicable for normal nonobstructed traffic:

thus

K K since the quotient K is independent from density fluctuations to a great extent, the following is true i: Measuring cross section j: Time interval The following is applicable for a locally fixed obstruction:

IK K =O Time constancy The following is applicable for moving obstructions:

IK K O obstruction Diagrams of the frequency distribution H of the time gaps are illustrated in FIG. 3. The solid line C repre sents the traffic flow of a given strength in the normal case, and the dotted line C the same traffic flow in the case of an obstruction. It can be seen from the diagrams that the true characteristic values, namely the mean value i(as the mean value of the time interval) and the variation or dispersion (as a measure or evaluation for the dispersion of the time in terval), change substantially according to the values 2' or S respectively.

In order to explain these changes, the surfaces F or F, respectively, were considered with the curves C or C, respectively, which, according to definition of or S, respectively amount to 75% of the entire surfaces of their associated curve C or C.

The surfaces F or F are equally large in the case of an equal number of observed vehicles. The nature of the shifting of the surfaces F or F, respec tively, is clearly defined by the magn itudes7and S or Z and S respectively, whereby or S represents the concentration of the surface upon the abscissa.

Finally, the extent of obstruction K upon a highway is illustrated in FIG. 4, wherein a distinction is made between areas with no traffic jam (not hatched) and the area where ajam is produced (cross-hatched). It will be noted therefrom that with the obstruction K for the area with nojam (not hatched), good measuring results are achieved with the aboved mentioned system. If, however, a traffic jam (cross-hatched area) occurs, the magnitude K will only supply valuable results up to a certain boundary value KG. In such case the loop occupation B can be introduced as an additional criteria, which will enable the achievement of a continuous supervision for all possible traffic conditions, including that involving the obstruction K.

Having thus described my invention, it is obvious that although minor modifications might be suggested by those versed in the art, it should be understood that I wish to embody within the scope of the patent warranted hereon all such modifications as reasonably and properly come within the scope of my contribution to the art.

I claim as my invention:

1. A system for monitoring traffic flow on streets having at least two traffic lanes free from oppositely di rccted traffic, particularly highways, wherein each traffic lane can be monitored, at least at one common monitoring location, by respective vehicle detectors, comprising for each detector a measuring system for deriving representative magnitudes of time intervals between successive vehicles at the associated detector, means for forming values representative of such magnitudes and comprising a mean value device to which interval magnitudes are supplied, and a memory for storing successive mean interval values derived from said mean value device, the output of said value forming means supplying such representative values, compari son means for effecting a predetermined comparison function between a plurality of representative values, and means operatively connecting corresponding outputs of the respective value-forming means of a plurality of said detectors to said comparison means for comparison of the respective representative values of said detectors, the output of said comparison means being operative to provide an evaluatable output magnitude related to the traffic flow.

2. A system according to claim 1, comprising in further combination, timing means, operatively connected with said measuring system, operable to simulate a vehicle by providing an impulse if time intervals of a certain magnitude are exceeded.

3. A system according to claim 1, wherein said com parison means comprises a quotient-forming device to which said representative values are supplied.

4. A system according to claim 1, wherein the representative values supplied to said comparison means are from different detectors of the same monitoring loca tion.

5. A system according to claim 4, wherein in further combination, a further means forming device is provided, to which the output of said said comparison means is supplied, the output value of which provides an evaluatable output magnitude.

6. A system according to claim 5, comprising in further combination a further memory for storing the output values of said further mean value forming device, further comparison means to which the output of said further memory is supplied, along with a similar output from another monitoring location, the output of such further comparison means providing an evaluatable output magnitude.

7. A system according to claim 6, wherein said further comparison means comprises a difference-forming means, the output of which supplies an evaluatable output magnitude.

8. A system according to claim 1, wherein said valueforming means for each vehicle detector includes means, to which are supplied other magnitudes differ ent from said first-mentioned magnitudes, but also representative of time intervals between respective vehicles at the associated detector, operative to modify such second magnitudes to form second corresponding representative values, a second mean value forming device to which said last-mentioned representative values are supplied, a second memory for storing successive mean values derived from said second means forming device, and linking means for effecting a predetermined comparison function between mean values in said second memory with the mean interval values stored in said first memory of the associated detector, the output magnitude of said last-mentioned means comprising the output of said value-forming means and supplied to said comparison means as the representative value of such detector, which is to be compared with a corresponding value from another one of said detector.

9. A system according to claim 8, whereifi the F638??- sentative magnitude supplied t said modify/ing ffiilh comprises a difference value Between the ereeeaiag mean interval value and the next interval value;

10. A system according to claim 8, wherein said linking means comprises a product-forming device.

1 1. A system according to claim 8, wherein said modifying means comprises a product forming device operative to form the square of such other representative magnitudes.

12. A system according to claim 8, wherein said modifying means comprises a product-forming device operative to form the square of such other representative magnitudes.

13. A system according to claim 8, wherein said first means value forming device is operable to also provide the difference value between a newly received interval magnitude and the mean value of the immediately previous interval, which difference value is modified by said modifying means and forms said second representative corresponding magnitude and which is supplied to said second mean value forming device, the linking means between the respective memories therefor and said comparison means including a productforming device to which the output values of such memories are supplied, said comparison means comprising a quotient-forming device to which the output value of said product-forming device is supplied, and to which is also supplied the output value derived from another of said detectors, the output value of such quotient-forming device being supplied to a further mean value forming device, the output value of which is supplied to one input of further comparison device means, the other input of which is connected by further linking means to memories associated with a plurality of other detectors.

14. A system according to claim 13, wherein means are provided for the respective mean value forming devices, for adding the product of a selected factor and the difference between the previously respectively stored mean value and the new measured value, to the stored old mean value.

15. A system according to claim 13, comprising in further combination, timing means, operatively connected with said measuring system, operable to simulate a vehicle by providing an impulse if time intervals of a certain magnitude are exceeded.

16. A system according to claim 13, wherein the output value supplied from said first comparison means to said further comparison means, is also supplied to additional comparison means, to which is supplied the immediately previous corresponding value from said lastmentioned further mean-forming device, the outputs of both said further and additional comparison means comprising evaluation magnitudes related to the traffic flow.

17. A system according to claim 16, wherein each of the mean-forming devices associated with the mean interval magnitude and the mean difference value has operatively connected thereto means for altering the associated difference value, between a new magnitude and the previous value, by a predetermined factor, the factors for the respective mean-forming devices having different values.

18. A system according to claim 17, wherein said modifying means comprises a product-forming device operative to form the square of such other representative magnitudes.

19. A system according to claim 18, wherein said difference forming device is operable to evaluate at predetermined times, the contents of memories of a monitoring location, and operatively connected with at least two associated traffic detectors.

20. A system according to claim 18, wherein said difference forming device is operable to evaluate the contents of memories of two monitoring locations which can be simultaneously supplied, under control of the timing means, and operatively connected with at least two associated traffic detectors.

21. A system according to claim 18, wherein the memories of a single monitoring location are interlinked by means of a quotient-forming device during the evaluation of only a like type of mean time values, and both memories of a detector are interlinked by means of a product forming device, in the case of a common evaluation of different types of mean time values.

22. A system according to claim 18, wherein means are provided for the respective mean value forming devices, for adding the product of a selected factor and the difference between the previously respectively stored mean value and the new measured value, to the stored old mean value.

23. A system according to claim 13, wherein said modifying means comprises a product-forming device operative to form the square of such other representative magnitudes. 

1. A system for monitoring traffic flow on streets having at least two traffic lanes free from oppositely directed traffic, particularly highways, wherein each traffic lane can be monitored, at least at one common monitoring location, by respective vehicle detectors, comprising for each detector a measuring system for deriving representative magnitudes of time intervals between successive vehicles at the associated detector, means for forming values representative of such magnitudes and comprising a mean value device to which interval magnitudes are supplied, and a memory for storing successive mean interval values derived from said mean value device, the output of said value forming means supplying such representative values, comparison means for effecting a predetermined comparison function between a plurality of representative values, and means operatively connecting corresponding outputs of the respective value-forming means of a plurality of said detectors to said comparison means for comparison of the respective representative values of said detectors, the output of said comparison means being operative to provide an evaluatable output magnitude related to the traffic flow.
 2. A system according to claim 1, comprising in further combination, timing means, operatively connected with said measuring system, operable to simulate a vehicle by providing an impulse if time intervals of a certain magnitude are exceeded.
 3. A system according to claim 1, wherein said comparison means comprises a quotient-forming device to which said representative values are supplied.
 4. A system according to claim 1, wherein the representative values supplied to said comparison means are from different detectors of the same monitoring location.
 5. A system according to claim 4, wherein in further combination, a further means forming device is provided, to which the output of said said comparison means is supplied, the output value of which provides an evaluatable output magnitude.
 6. A system according to claim 5, comprising in further Combination a further memory for storing the output values of said further mean value forming device, further comparison means to which the output of said further memory is supplied, along with a similar output from another monitoring location, the output of such further comparison means providing an evaluatable output magnitude.
 7. A system according to claim 6, wherein said further comparison means comprises a difference-forming means, the output of which supplies an evaluatable output magnitude.
 8. A system according to claim 1, wherein said value-forming means for each vehicle detector includes means, to which are supplied other magnitudes different from said first-mentioned magnitudes, but also representative of time intervals between respective vehicles at the associated detector, operative to modify such second magnitudes to form second corresponding representative values, a second mean value forming device to which said last-mentioned representative values are supplied, a second memory for storing successive mean values derived from said second means forming device, and linking means for effecting a predetermined comparison function between mean values in said second memory with the mean interval values stored in said first memory of the associated detector, the output magnitude of said last-mentioned means comprising the output of said value-forming means and supplied to said comparison means as the representative value of such detector, which is to be compared with a corresponding value from another one of said detector.
 9. A system according to claim 8, wherein the representative magnitude supplied to said modifying means comprises a difference value between the preceding mean interval value and the next interval value.
 10. A system according to claim 8, wherein said linking means comprises a product-forming device.
 11. A system according to claim 8, wherein said modifying means comprises a product forming device operative to form the square of such other representative magnitudes.
 12. A system according to claim 8, wherein said modifying means comprises a product-forming device operative to form the square of such other representative magnitudes.
 13. A system according to claim 8, wherein said first means value forming device is operable to also provide the difference value between a newly received interval magnitude and the mean value of the immediately previous interval, which difference value is modified by said modifying means and forms said second representative corresponding magnitude and which is supplied to said second mean value forming device, the linking means between the respective memories therefor and said comparison means including a product-forming device to which the output values of such memories are supplied, said comparison means comprising a quotient-forming device to which the output value of said product-forming device is supplied, and to which is also supplied the output value derived from another of said detectors, the output value of such quotient-forming device being supplied to a further mean value forming device, the output value of which is supplied to one input of further comparison device means, the other input of which is connected by further linking means to memories associated with a plurality of other detectors.
 14. A system according to claim 13, wherein means are provided for the respective mean value forming devices, for adding the product of a selected factor and the difference between the previously respectively stored mean value and the new measured value, to the stored old mean value.
 15. A system according to claim 13, comprising in further combination, timing means, operatively connected with said measuring system, operable to simulate a vehicle by providing an impulse if time intervals of a certain magnitude are exceeded.
 16. A system according to claim 13, wherein the output value supplied from said first comparison means to said further comparison means, is also supplied to additional cOmparison means, to which is supplied the immediately previous corresponding value from said last-mentioned further mean-forming device, the outputs of both said further and additional comparison means comprising evaluation magnitudes related to the traffic flow.
 17. A system according to claim 16, wherein each of the mean-forming devices associated with the mean interval magnitude and the mean difference value has operatively connected thereto means for altering the associated difference value, between a new magnitude and the previous value, by a predetermined factor, the factors for the respective mean-forming devices having different values.
 18. A system according to claim 17, wherein said modifying means comprises a product-forming device operative to form the square of such other representative magnitudes.
 19. A system according to claim 18, wherein said difference forming device is operable to evaluate at predetermined times, the contents of memories of a monitoring location, and operatively connected with at least two associated traffic detectors.
 20. A system according to claim 18, wherein said difference forming device is operable to evaluate the contents of memories of two monitoring locations which can be simultaneously supplied, under control of the timing means, and operatively connected with at least two associated traffic detectors.
 21. A system according to claim 18, wherein the memories of a single monitoring location are interlinked by means of a quotient-forming device during the evaluation of only a like type of mean time values, and both memories of a detector are interlinked by means of a product forming device, in the case of a common evaluation of different types of mean time values.
 22. A system according to claim 18, wherein means are provided for the respective mean value forming devices, for adding the product of a selected factor and the difference between the previously respectively stored mean value and the new measured value, to the stored old mean value.
 23. A system according to claim 13, wherein said modifying means comprises a product-forming device operative to form the square of such other representative magnitudes. 